1. Waves

2. Waves Transport energy over a body of waterTransport energy over a body of water

3. Waves Origin and Type Wind waves – “wind-generated”Wind waves – “wind-generated” Seiche – “pressure-generated”Seiche – “pressure-generated” Tsunami – “seismic-generated”Tsunami – “seismic-generated” Tide – “gravity-generated”Tide – “gravity-generated”

4. Wave Terminology Still water line – level of ocean if it were flat w/o wavesStill water line – level of ocean if it were flat w/o waves Crest – highest part of waveCrest – highest part of wave Trough – lowest part of waveTrough – lowest part of wave Amplitude – distance between crest and still water lineAmplitude – distance between crest and still water line Wave height (H) – vertical distance between crest and troughWave height (H) – vertical distance between crest and trough Wavelength (L) – horizontal distance from each crest or each troughWavelength (L) – horizontal distance from each crest or each trough – ½ the wave height – Or any point with the same successive point Still water line Height Steepness = Height (H)/length (L)Steepness = Height (H)/length (L)

5. Wave Parameters Period (T) – the time it takes for two successive waves to pass a particular pointPeriod (T) – the time it takes for two successive waves to pass a particular point Frequency (f) – the # of waves that pass a particular point in any given time periodFrequency (f) – the # of waves that pass a particular point in any given time period

6. Deep Water Wave Motion Water particles move in orbitsWater particles move in orbits Particle motion ceases at ½ wavelengthParticle motion ceases at ½ wavelength Diameter of orbits decrease with depthDiameter of orbits decrease with depth Waves transmit energy, not water massWaves transmit energy, not water mass

7. Waves Types Deep Water Deep Water Shallow WaterShallow Water – H 2 O depth is >1/2 wavelength – Depth is <1/20 wavelength

8. Orbital Motion When under a wave crestWhen under a wave crest – Water moves up and forward When under a troughWhen under a trough – Water moves down and back Thus, water particles do not move forwardThus, water particles do not move forward – They move in circles

9. Waves Velocity The longer the wavelength, the faster the wave travelsThe longer the wavelength, the faster the wave travels Velocity (V) = wavelength (L)/Period (T)Velocity (V) = wavelength (L)/Period (T) For example:For example: – If T= 10 sec; L = 100 m – Then 100 m/10 sec. = 10 m/sec

10. Waves Generation Generated by ForceGenerated by Force – Sea Wrinkles  ripples  wind waves  swells Generated at storm centersGenerated at storm centers Separation of waves by differing rates of travel - dispersionSeparation of waves by differing rates of travel - dispersion – wind or air

11. Waves Size Factors determining size:Factors determining size: º Fetch º Wind velocity º Duration – Distance wind blows over open ocean – Speed of wind – Length of time wind blows

12. Waves Dispersion Wave train – a set of waves with the same wavelengthWave train – a set of waves with the same wavelength Individual waves move faster than wave trainIndividual waves move faster than wave train – wave dies out at front of train while new waves form at rear Wave train travels half the speed of individual waveWave train travels half the speed of individual wave

13. Wave Interference Combination of wavesCombination of waves – Build from one another = Constructive – Cancel each other = Destructive

14. Shallow Water Waves 3. Orbits progressively flatten at depth 6. Just above seafloor particles move in back-and-forth motion 4. Wave height (H) increases and wavelength (L) decreases 1. Swell feels bottom at depth < ½ wavelength 2. Wave crest peaks and wave slows 5. Wave breaks when H/L ratio > 1/7

15. Breaking Waves

16. Breaking waves Types Depends on steepnessDepends on steepness Type of Breakers:Type of Breakers: (a) Spilling (b) Plunging (c) Surging – Gentle slopes – Rolls onto beach – Surf gently rolls over the front – Moderately steep slope – Wave curls forming a tunnel – Steep slope

17. Waves Characteristics RefractionRefraction – Bending of waves – Waves approach shore at angle and drags – Feels bottom first and slows DiffractionDiffraction – As waves pass through small opening, waves spread

18. Seiches Standing wave oscillatesStanding wave oscillates Stationary point (node)Stationary point (node) Occurs in enclosed basins and/or lakesOccurs in enclosed basins and/or lakes Rise and fall of water levelRise and fall of water level

19. Tsunamis Giant sea waves generated by earthquakesGiant sea waves generated by earthquakes

20. Tsunami Causes EarthquakeEarthquake VolcanoesVolcanoes LandslidesLandslides Meteor impactMeteor impact

21. Tsunami Characteristics Shallow water waveShallow water wave Energy passes through entire water columnEnergy passes through entire water column Long periods (T)Long periods (T) long wavelengths (L)long wavelengths (L) Travel at great speedsTravel at great speeds Deep wave baseDeep wave base – T = 10-20 min. – L = 100-200 km – c = 200 m/s Small Height (H)Small Height (H) – H = 1-2 m

22. Tsunami Crest and Trough

23. Historical Tsunamis 1883 Krakatau Explosive volcanoExplosive volcano Large landmasses fell into the oceanLarge landmasses fell into the ocean 36,000 people killed by tsunami36,000 people killed by tsunami Today

24. Historical Tsunamis 1946 Pacific Tsunami Aleutian Island EarthquakeAleutian Island Earthquake Killed 165 people in HawaiiKilled 165 people in Hawaii Resulted in the creation of the 1 st “tsunami warning system”Resulted in the creation of the 1 st “tsunami warning system”

25. Historical Tsunamis 2004 Indonesian Tsunami 9.0 M earthquake9.0 M earthquake Deadliest tsunami ever recordedDeadliest tsunami ever recorded >260,000 people killed>260,000 people killed